HTTP/1.0
Hypertext Transfer Protocol -- HTTP/1.0
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Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol with the lightness and speed necessary for distributed,
collaborative, hypermedia information systems. It is a generic,
stateless, object-oriented protocol which can be used for many
tasks, such as name servers and distributed object management
systems, through extension of its request methods (commands). A
feature of HTTP is the typing and negotiation of data
representation, allowing systems to be built independently of the
data being transferred.
HTTP has been in use by the World-Wide Web global information
initiative since 1990. This specification reflects preferred usage
of the protocol referred to as "HTTP/1.0", and is compatible with
the most commonly used HTTP server and client programs implemented
prior to November 1994.
Table of Contents
1. Introduction
1.1 Purpose
1.2 Overall Operation
1.3 Terminology
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
2.2 Basic Rules
3. HTTP Message
3.1 Header Fields
3.2 Object Body
4. Usage of RFC 822 and MIME Constructs
4.1 Date/Time Format
4.2 Media Types
4.2.1 Multipart Types
4.2.1.1 Multipart/mixed
4.2.1.2 Multipart/parallel
4.2.1.3 Other Multipart Types
4.2.2 Conversion to Canonical Form
4.3 General Message Header Fields
4.3.1 Connection
4.3.2 Date
4.3.3 Forwarded
4.3.4 Mandatory
4.3.5 Message-ID
4.3.6 MIME-Version
5. Request
5.1 Request-Line
5.2 Method
5.2.1 GET
5.2.2 HEAD
5.2.3 POST
5.2.4 PUT
5.2.5 DELETE
5.2.6 LINK
5.2.7 UNLINK
5.3 HTTP-Version
5.4 Universal Resource Identifier
5.5 Request Header Fields
5.5.1 User-Agent
5.5.2 If-Modified-Since
5.5.3 Pragma
5.5.4 Authorization
5.5.5 Proxy-Authorization
5.5.6 Referer
5.5.7 From
5.5.8 Accept
5.5.9 Accept-Encoding
5.5.10 Accept-Language
6. Response
6.1 Status-Line
6.2 HTTP Version
6.3 Status Codes and Reason Phrases
6.3.1 Successful 2xx
6.3.2 Redirection 3xx
6.3.3 Client Error 4xx
6.3.4 Server Errors 5xx
6.4 Response Header Fields
6.4.1 Server
6.4.2 WWW-Authenticate
6.4.3 Proxy-Authenticate
6.4.4 Retry-After
7. Object Header Fields
7.1 Allow
7.2 Content-Length
7.3 Content-Type
7.4 Content-Encoding
7.5 Content-Transfer-Encoding
7.6 Content-Language
7.7 Expires
7.8 Last-Modified
7.9 URI Header
7.10 Location
7.11 Version
7.12 Derived-From
7.13 Title
7.14 Link
8. HTTP Negotiation Algorithm
9. Basic Access Authentication Scheme
10. Registration Authority
11. Security Considerations
11.1 Authentication of Clients
11.2 Idempotent Methods
11.3 Abuse of Server Log Information
12. Acknowledgments
13. References
14. Authors Addresses
Appendix A. Tolerant Applications
A.1 Request-Line, Status-Line, and Header Fields
A.2 Object Body
A.3 Backward Compatibility
1. Introduction
1.1 Purpose
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol with the lightness and speed necessary for distributed,
collaborative, hypermedia information systems. HTTP has been in use
by the World-Wide Web global information initiative since 1990.
This specification reflects preferred usage of the protocol
referred to as "HTTP/1.0". This specification does not necessarily
reflect the "current practice" of any single HTTP server or client
implementation. It does, however, seek to remain compatible with
existing implementations wherever possible, and should be
considered the reference for future implementations of HTTP/1.0.
Practical information systems require more functionality than
simple retrieval, including search, front-end update, and
annotation. HTTP/1.0 allows an open-ended set of methods to be used
to indicate the purpose of a request. It builds on the discipline
of reference provided by the Universal Resource Identifier
(URI) [2], as a location (URL) [3] or name (URN), for indicating
the resource on which a method is to be applied. Messages are
passed in a format similar to that used by Internet Mail [7] and
the Multipurpose Internet Mail Extensions (MIME) [4].
HTTP/1.0 is also used for communication between user agents and
various gateways, allowing hypermedia access to existing Internet
protocols like SMTP [12], NNTP [11], FTP [14], Gopher [1], and
WAIS [8]. HTTP/1.0 is designed to allow such gateways, via proxy
servers, without any loss of the data conveyed by those earlier
protocols.
1.2 Overall Operation
The HTTP protocol is based on a request/response paradigm. A
requesting program (termed a client) establishes a connection with
a receiving program (termed a server) and sends a request to the
server in the form of a request method, URI, and protocol version,
followed by a MIME-like message containing request modifiers,
client information, and possible body content. The server responds
with a status line (including its protocol version and a success or
error code), followed by a MIME-like message containing server
information, object metainformation, and possible body content. It
should be noted that a given program may be capable of being both a
client and a server; our use of those terms refers only to the role
being performed by the program during a particular connection,
rather than to the program's purpose in general.
On the Internet, the communication generally takes place over a
TCP/IP connection. The default port is TCP 80 [15], but other ports
can be used. This does not preclude the HTTP/1.0 protocol from
being implemented on top of any other protocol on the Internet, or
on other networks. The mapping of the HTTP/1.0 request and response
structures onto the transport data units of the protocol in
question is outside the scope of this specification.
For most current implementations, the connection is established by
the client prior to each request and closed by the server after
sending the response. However, this is not a feature of the
protocol and is not required by this specification. Both clients
and servers must be capable of handling cases where either party
closes the connection prematurely, due to user action, automated
time-out, or program failure. In any case, the closing of the
connection by either or both parties always terminates the current
request, regardless of its status.
1.3 Terminology
This specification uses a number of terms to refer to the roles
played by participants in, and objects of, the HTTP communication.
connection
A virtual circuit connecting two parties for the purpose of
communication.
request
An HTTP request message (as defined in Section 5).
response
An HTTP response message (as defined in Section 6).
resource
A network data object or service which can be identified by a
URI.
client
A program that establishes connections for the purpose of
sending requests.
user agent
The client program which is closest to the user and which
initiates requests at their behest.
server
A program that accepts connections in order to service requests
by sending back responses.
origin server
The server on which a given resource resides or is to be created.
proxy
An intermediary program which acts as both a server and a client
for the purpose of forwarding requests. Proxies are often used
to act as a portal through a network firewall. A proxy server
accepts requests from other clients and services them either
internally or by passing them (with possible translation) on to
other servers. A caching proxy is a proxy server with a local
cache of server responses -- some requested resources can be
serviced from the cache rather than from the origin server. Some
proxy servers also act as origin servers.
gateway
A proxy which services HTTP requests by translation into
protocols other than HTTP. The reply sent from the remote server
to the gateway is likewise translated into HTTP before being
forwarded to the user agent.
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
All of the mechanisms specified in this document are described in
both prose and an augmented Backus-Naur Form (BNF) similar to that
used by RFC 822 [7]. Implementors will need to be familiar with the
notation in order to understand this specification. The augmented
BNF includes the following constructs:
name = definition
The name of a rule is simply the name itself (without any
enclosing "<" and ">") and is separated from its definition by
the equal character "=". Whitespace is only significant in that
indentation of continuation lines is used to indicate a rule
definition that spans more than one line. Certain basic rules
are in uppercase, such as SP, TAB, CRLF, DIGIT, ALPHA, etc.
Angle brackets are used within definitions whenever their
presence will facilitate discerning the use of rule names.
"literal"
Quotation marks surround literal text. Unless stated otherwise,
the text is case-insensitive.
rule1 | rule2
Elements separated by a bar ("|") are alternatives, e.g.
"yes | no" will accept yes or no.
(rule1 rule2)
Elements enclosed in parentheses are treated as a single
element. Thus,"(elem (foo | bar) elem)" allows the token
sequences "elem foo elem" and "elem bar elem".
*rule
The character "*" preceding an element indicates repetition. The
full form is "<n>*<m>element" indicating at least <n> and at
most <m> occurrences of element. Default values are 0 and
infinity so that "*(element)" allows any number, including zero;
"1*element" requires at least one; and "1*2element" allows one
or two.
[rule]
Square brackets enclose optional elements; "[foo bar]" is
equivalent to "*1(foo bar)".
N rule
Specific repetition: "<n>(element)" is equivalent to
"<n>*<n>(element)"; that is, exactly <n> occurrences of
(element). Thus 2DIGIT is a 2-digit number, and 3ALPHA is a
string of three alphabetic characters.
#rule
A construct "#" is defined, similar to "*", for defining lists
of elements. The full form is "<n>#<m>element" indicating at
least <n> and at most <m> elements, each separated by one or
more commas (",") and optional linear whitespace (LWS). This
makes the usual form of lists very easy; a rule such as
"( *LWS element *( *LWS "," *LWS element ))" can be shown as
"1#element". Wherever this construct is used, null elements are
allowed, but do not contribute to the count of elements present.
That is, "(element), , (element)" is permitted, but counts as
only two elements. Therefore, where at least one element is
required, at least one non-null element must be present. Default
values are 0 and infinity so that "#(element)" allows any
number, including zero; "1#element" requires at least one; and
"1#2element" allows one or two.
; comment
A semi-colon, set off some distance to the right of rule text,
starts a comment that continues to the end of line. This is a
simple way of including useful notes in parallel with the
specifications.
2.2 Basic Rules
The following rules are used throughout this specification to
describe basic parsing constructs. The US-ASCII character set is
defined in [17].
OCTET = <any 8-bit character>
CHAR = <any US-ASCII character (octets 0 - 127)>
UPALPHA = <any US-ASCII uppercase letter "A".."Z">
LOALPHA = <any US-ASCII lowercase letter "a".."z">
ALPHA = UPALPHA | LOALPHA
DIGIT = <any US-ASCII digit "0".."9">
CTL = <any US-ASCII control character
(octets 0 - 31) and DEL (127)>
CR = <US-ASCII CR, carriage return (13)>
LF = <US-ASCII LF, linefeed (10)>
SP = <US-ASCII SP, space (32)>
HTAB = <US-ASCII HT, horizontal-tab (9)>
<"> = <US-ASCII double-quote mark>
HTTP/1.0 defines the character sequence CR LF as the end-of-line
marker for all protocol elements except the Object-Body (see
Appendix A for tolerant applications). The end-of-line marker for
an Object-Body is defined by its associated media type, as
described in Section 4.2.2.
CRLF = CR LF
HTTP/1.0 headers can be folded onto multiple lines if the
continuation lines begin with linear whitespace characters. All
linear whitespace (including folding) has the same semantics as SP.
LWS = [CRLF] ( SP | HTAB )
Many HTTP/1.0 header field values consist of words separated by LWS
or special characters. These special characters must be in a quoted
string to be used within a parameter value.
word = token | quoted-string
token = 1*<any CHAR except CTLs or tspecials>
tspecials = "(" | ")" | "<" | ">" | "@"
| "," | ";" | ":" | "¥" | <">
| "/" | "[" | "]" | "?" | "="
| SP | HTAB
A string of text is parsed as a single word if it is quoted using
double-quote marks or angle brackets.
quoted-string = ( <"> *(qdtext) <"> )
| ( "<" *(qatext) ">" )
qdtext = <any CHAR except <"> and CTLs,
but including LWS>
qatext = <any CHAR except "<", ">", and CTLs,
but including LWS>
The text rule is only used for descriptive field contents. Words of
*text may contain characters from character sets other than US-ASCII
only when encoded according to the rules of RFC 1522 [5].
text = <any OCTET except CTLs,
but including LWS>
3. HTTP Message
HTTP messages consist of requests from client to server and
responses from server to client.
HTTP-message = Simple-Request ; HTTP/0.9 messages
| Simple-Response
| Full-Request ; HTTP/1.0 messages
| Full-Response
Full-Request and Full-Response use the generic message format of
RFC 822 [7] for transferring objects. Both messages may include
optional header fields (a.k.a. "headers") and an object body. The
object body is separated from the headers by a null line (i.e., a
line with nothing preceding the CRLF).
Full-Request = Request-Line ; see Section 5.1
*General-Header ; see Section 4.3
*Request-Header ; see Section 5.5
*Object-Header ; see Section 7
CRLF
[ Object-Body ]
Full-Response = Status-Line ; see Section 6.1
*General-Header ; see Section 4.3
*Response-Header ; see Section 6.4
*Object-Header ; see Section 7
CRLF
[ Object-Body ]
Simple-Request and Simple-Response, as defined in Section 5 and
Section 6 respectively, do not allow the use of any header
information and are limited to a single request method (GET). This
prevents the client from using content negotiation and the server
from identifying the media type of the returned object. Therefore,
clients are discouraged from using the Simple-Request format except
for the simplest of applications.
3.1 Header Fields
HTTP header fields, which include Request-Header, Response-Header,
General-Header, Object-Header, and extension fields, follow the
same generic format as that given in Section 3.1 of RFC 822 [7].
Each header field consists of a name followed by a colon (":") and
the field value. The field value may be preceded by any amount of
linear-white-space, though a single SP is preferred. Header fields
can be extended over multiple lines by preceding each extra line
with one or more linear white-space characters.
HTTP-header = field-name ":" [ field-value ] CRLF
field-name = 1*<any CHAR, excluding CTLs, SP, and ":">
field-value = *( field-content | comment | LWS )
field-content = <the OCTETs making up the field-value
and consisting of either *text or combinations
of token, tspecials, and quoted-string>
The order in which header fields are received is not significant.
However, it is considered "good practice" to send General-Header
fields first, followed by Request-Header or Response-Header fields
prior to the Object-Header fields. Comments can be included in HTTP
header fields by surrounding the comment text with parentheses.
comment = "(" *( ctext | comment ) ")"
ctext = <any text excluding "(" and ")">
Note: Use of comments within HTTP headers is generally
discouraged, since they are rarely seen by human eyes and
hence only increase network traffic. However, they may be
useful for messages posted or retrieved via NNTP and SMTP
gateways.
3.2 Object Body
The object body (if any) sent with an HTTP/1.0 request or response
is in a format and encoding defined by the Object-Header fields.
Object-Body = *OCTET
The actual length, encoding, and data type of the Object-Body is
determined via the header fields Content-Length, Content-Encoding,
Content-Transfer-Encoding, and Content-Type, similar to those
defined by MIME [4]. If the Content-Length header field is present,
its value in bytes (number of octets) represents the length of the
Object-Body. Otherwise, the body length is determined either by a
heuristic function of the Content-Type and Content-Encoding, or by
the closing of the connection by the server.
Note: Closing the connection cannot be used to indicate the
value of the Content-Length header when the Object-Body is
part of a request message, as it leaves no possibility for
the server to send back a response.
4. Usage of RFC 822 and MIME Constructs
HTTP/1.0 reuses many of the constructs defined for Internet Mail
(RFC 822, [7]) and the Multipurpose Internet Mail Extensions
(MIME, [4]) to allow Object's to be transmitted in an open variety
of representations. However, because it is not limited by the
restrictions of existing mail protocols and gateways, HTTP does not
obey some of the constraints imposed by RFC 822 and MIME for mail
transport. This section describes how these common constructs are
defined within HTTP.
4.1 Date/Time Format
For historical reasons, HTTP/1.0 allows three different formats for
the representation of date/time stamps:
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
The first format is preferred as an Internet standard and
represents a fixed-length subset of that defined by RFC 1123 [6]
(an update to RFC 822 [7]). The second format is in common use
today, but is based on the obsolete RFC 850 [10] date format and
lacks a four-digit year. HTTP/1.0 clients and servers must accept
all three formats, though they should never generate the third
(asctime) format. It is strongly recommended that future clients
and servers only generate the RFC 1123 format for representing
date/time stamps in HTTP/1.0 requests and responses.
All HTTP/1.0 date/time stamps must be represented in Universal Time
(UT), also known as Greenwich Mean Time (GMT), without exception.
This is indicated in the first two formats by the inclusion of
"GMT" as the three-letter abbreviation for time zone, and should be
assumed when reading the asctime format.
HTTP-date = rfc1123-date | rfc850-date | asctime-date
rfc1123-date = wkday "," SP date1 SP time SP "GMT"
rfc850-date = weekday "," SP date2 SP time SP "GMT"
asctime-date = wkday SP date3 SP time SP 4DIGIT
date1 = 2DIGIT SP month SP 4DIGIT
; day month year (e.g. 02 Jun 1982)
date2 = 2DIGIT "-" month "-" 2DIGIT
; day-month-year (e.g. 02-Jun-82)
date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
; month day (e.g. Jun 2)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; 00:00:00 - 23:59:59
wkday = "Mon" | "Tue" | "Wed"
| "Thu" | "Fri" | "Sat" | "Sun"
weekday = "Monday" | "Tuesday" | "Wednesday"
| "Thursday" | "Friday" | "Saturday" | "Sunday"
month = "Jan" | "Feb" | "Mar" | "Apr"
| "May" | "Jun" | "Jul" | "Aug"
| "Sep" | "Oct" | "Nov" | "Dec"
Note: HTTP/1.0 requirements for the date/time stamp format
apply only to their usage within the protocol stream.
Clients and servers are not required to use these formats
for user presentation, request logging, etc.
4.2 Media Types
HTTP uses Internet Media Types [13], formerly referred to as MIME
Content-Types [4], in order to provide open and extensible data
typing and type negotiation. For mail applications, where there is
no type negotiation between sender and receiver, it is reasonable
to put strict limits on the set of allowed media types. With HTTP,
however, user agents can identify acceptable media types as part of
the connection, and thus are allowed more freedom in the use of non-
registered types. The following grammar for media types is a
superset of that for MIME.
media-type = type "/" subtype *( ";" parameter )
type = token ; case-insensitive
subtype = token ; case-insensitive
parameter = attribute "=" value
attribute = token ; case-insensitive
value = token | quoted-string ; sometimes
; case-sensitive
4.2.1 Multipart Types
HTTP provides for a number of "multipart" types -- encapsulations of
several object body parts within a single message's Object-Body.
Multipart responses should only be used in responses when the user
agent has indicated acceptability of the multipart type in addition
to the media types of each constituent body part. User agents may
use multipart types when submitting objects as part of a POST or
PUT request.
As in MIME [4], all multipart types share a common syntax and must
include a boundary parameter as part of the media-type. Unlike in
MIME, multipart body parts may contain HTTP header fields which are
significant to the meaning of that part.
boundary = 0*69( bchar | SP ) bchar
bchar = DIGIT | ALPHA | "'" | "(" | ")" | "+"
| "_" | "," | "-" | "." | "/" | ":" | "=" | "?"
The Object-Body of a multipart message is specified as follows:
multipart-body = discard-text 1*encapsulation
close-delimiter discard-text
encapsulation = delimiter body-part CRLF
delimiter = "--" boundary CRLF ; boundary is obtained
; from Content-Type.
close-delimiter= "--" boundary "--" CRLF
discard-text = *(*text CRLF) ; ignored
body-part = *Object-Header
CRLF
[ Object-Body ] ; May be recursive
; if boundary differs
A URI-header field (Section 7.9) should be included in the body-
part for each enclosed object that can be identified by a URI.
4.2.1.1 Multipart/mixed
The "multipart/mixed" media type is used when the first body-part
contains references to other parts which the sender wishes to send
at the same time. For example, the first body-part could be an HTML
document and the following body-parts could be annotations upon
that document. However, the use of "multipart/mixed" is strongly
discouraged in cases where the related objects are likely to have
already been retrieved and cached by a user agent or caching proxy.
4.2.1.2 Multipart/parallel
The "multipart/parallel" media type is identical to
"multipart/mixed", but with the additional semantics that the parts
should be presented simultaneously by the user agent. This media
type would be appropriate for situations where simultaneous
presentation is an important aspect of the information, such as for
audio-annotated slides and movies.
Note: This document does not define what is meant by
"simultaneous presentation." That is, HTTP/1.0 does not
provide any means of synchronization between the parts in
messages of type "multipart/parallel".
4.2.1.3 Other Multipart Types
The other multipart types registered by IANA [15] do not have any
special meaning for HTTP/1.0, though user agents may need to
understand each type in order to correctly interpret the purpose of
each body-part.
4.2.2 Conversion to Canonical Form
Regardless of the media type, HTTP does not require any conversion
to canonical form of line terminators or other constructs in the
Object-Body while it is being transferred between an HTTP client
and server. However, gateway applications must understand that,
before an HTTP Object-Body can passed to a MIME-conforming
protocol, conversion to canonical form may be necessary [4].
Furthermore, additional processing may be required in order to
convert an HTTP message to something that can be transferred via
other protocols, particularly when a Content-Encoding has been
applied to the enclosed object.
In contrast, no conversion should be necessary for a MIME-
conforming message to be tranferred using HTTP.
4.3 General Message Header Fields
There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the
communicating parties or the object being transferred. Although
none of the General-Header fields are required, they are all
strongly recommended where their use is appropriate, and should be
understood by all future HTTP/1.0 clients and servers. These
headers apply only to the message being transmitted.
General-Header = Connection
| Date
| Forwarded
| Mandatory
| Message-ID
| MIME-Version
4.3.1 Connection
The Connection header is used to specify the parameters (desired or
actual) of the current connection. Clients can use this header to
indicate their desire to use a set of connection options. Servers
can use this header to indicate what options are actually being
applied. This field applies only to the current connection --
receivers should not cache or otherwise save the connection
information after the connection is closed. Proxies must not
forward this header, though they may generate a separate Connection
header for their own connections.
Connection = "Connection" ":" 1#connect-option
connect-option = token [ "=" word ]
Although current HTTP/1.0 clients and servers do not make use of
the Connection header outside of experiments, this field will be
necessary to enable future extensibility of connection-specific
behavior. Most importantly, HTTP/1.0 proxies need to know that they
must not forward this header even when they do not understand or
make use of its contents. For example, an experimental client may
send:
Connection: keep-alive
to indicate that it desires to keep the connection open for
multiple requests. The server may then respond with a message
containing:
Connection: keep-alive, timeout=10, maxreq=5
to indicate that the connection will be kept open for a maximum of
5 requests, but will timeout if the next request is not received
within 10 seconds. Note that the semantics of these options are not
defined for HTTP/1.0, though similar options may be defined by
future versions of HTTP.
4.3.2 Date
The Date header represents the date and time at which the message
was originated, having the same semantics as orig-date in RFC 822.
If a message is received via direct connection with the user agent
(in the case of requests) or the origin server (in the case of
responses), then the default date can be assumed to be the current
date at the receiving end. However, since the date--as it is
believed by the origin--is important for evaluating cached
responses, origin servers should always include a Date header. A
received message which does not have a Date header field should be
assigned one by the receiver if and only if the message will be
cached by that receiver or gatewayed via a protocol which requires
a Date. The field value is an HTTP-date, as described in Section
4.1.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
Only one Date header field is allowed per message.
Note: An earlier version of this document incorrectly
specified that this field should contain the creation date
of the enclosed Object-Body. This has been changed to
reflect actual (and proper) usage.
4.3.3 Forwarded
The Forwarded header is to be used by proxies to indicate the
intermediate steps between the user agent and the server (on
requests) and between the origin server and the client (on
responses). It is analogous to the "Received" field of RFC 822 and
is intended to be used for tracing transport problems and avoiding
request loops.
Forwarded = "Forwarded" ":" "by" URI [ "(" product ")" ]
[ "for" FQDN ]
FQDN = <Fully-Qualified Domain Name>
For example, a message could be sent from a client on
ptsun00.cern.ch to a server at www.ics.uci.edu port 80, via an
intermediate HTTP proxy at info.cern.ch port 8000. The request
received by the server at www.ics.uci.edu would then have the
following Forwarded header field:
Forwarded: by http://info.cern.ch:8000/ for ptsun00.cern.ch
Multiple Forwarded header fields are allowed and should represent
each proxy that has forwarded the message. It is strongly
recommended that proxies used as a portal through a network
firewall do not, by default, send out information about the
internal hosts within the firewall region. This information should
only be propagated if explicitly enabled. If not enabled, the for
token and FQDN should not be included in the field value.
4.3.4 Mandatory
The Mandatory header is used to indicate a list of other header
field names which must be understood by the receiver before the
contents of the message can be stored, cached, or presented to a
user. This header is used to alert the receiver that, unlike the
default behavior, it cannot safely ignore the semantics of the
listed field-names if they are not understood. It is anticipated
that the field names correspond to conditions that must be met by
the receiver in order to abide by the sender's licensing,
copyright, payment, or other fair-usage constraints.
Mandatory = "Mandatory" ":" 1#field-name
Recommended usage of the Mandatory header is not defined for
HTTP/1.0. However, caching proxies must not cache responses which
contain mandatory header information which is not understood by the
proxy.
4.3.5 Message-ID
The Message-ID field in HTTP is identical to that used by Internet
Mail and USENET messages, as defined in [10]. That is, it gives the
message a single, unique identifier which can be used for
identifying the message (not its contents) for "much longer" than
the expected lifetime of that message.
Message-ID = "Message-ID" ":" "<" addr-spec ">"
addr-spec = unique-string "@" FQDN
unique-string = <1*CHAR, not including whitespace, "@", or ">">
where unique-string must be unique within the host specified by
FQDN. An example is
Message-ID: <9411151630.4256@info.cern.ch>
which is composed using the time, date and process-ID on the host
info.cern.ch.
4.3.6 MIME-Version
HTTP is not a MIME-conformant protocol. However, HTTP/1.0 messages
may include a single MIME-Version header field to indicate what
version of the MIME protocol was used to construct the message. Use
of the MIME-Version header field should indicate that the message
is in full compliance with the MIME protocol (as defined in [4]).
Unfortunately, current versions of HTTP/1.0 clients and servers use
this field indiscriminantly, and thus receivers must not take it
for granted that the message is indeed in full compliance with
MIME. Gateways are responsible for ensuring this compliance (where
possible) when exporting HTTP messages to strict MIME environments.
Future HTTP/1.0 applications must only use MIME-Version when the
message is intended to be MIME-conformant.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.0. However,
HTTP/1.0 message parsing and semantics are defined by this document
and not the MIME specification.
5. Request
A request message from a client to a server includes, within the
first line of that message, the method to be applied to the object
requested, the identifier of the object, and the protocol version
in use. For backwards compatibility with the more limited HTTP/0.9
protocol, there are two valid formats for an HTTP request:
Request = Simple-Request | Full-Request
Simple-Request = "GET" SP URI CRLF ; HTTP/0.9 request
Full-Request = Request-Line ; see Section 5.1
*General-Header ; see Section 4.3
*Request-Header ; see Section 5.5
*Object-Header ; see Section 7
CRLF
[ Object-Body ] ; see Section 3.2
If an HTTP/1.0 server receives a Simple-Request, it must respond
with an HTTP/0.9 Simple-Response. Similarly, if a client receives a
response that does not begin with a Status-Line, it should assume
that the response is a Simple-Response and parse it accordingly.
5.1 Request-Line
The Request-Line begins with a method token, followed by the URI
and the protocol version, and ending with CRLF. The elements are
separated by SP characters. No CR or LF are allowed except in the
final CRLF sequence.
Request-Line = Method SP URI SP HTTP-Version CRLF
5.2 Method
The Method token indicates the method to be performed on the
resource identified by the URI. The method is case-sensitive and
extensible.
Method = "GET" | "HEAD" | "PUT" | "POST"
| "DELETE" | "LINK" | "UNLINK"
| extension-method
extension-method=token
The methods GET and HEAD must be supported by all conforming
HTTP/1.0 servers. The list of methods acceptable by a specific
resource can be specified in an "Allow" Object-Header (Section
7.1). However, the client is always notified through the return
code of the response whether a method is currently allowed on a
specific resource, as this can change dynamically. The set of
common methods for HTTP/1.0 is described below. Although this set
can be easily expanded, additional methods cannot be assumed to
share the same semantics for separately extended clients and
servers. In order to maintain compatibility, the semantic
definition for extension methods should be registered with the HTTP
registration authority (Section 10). Servers should return the
Status-Code "501 Not Implemented" if the method is unknown.
5.2.1 GET
The GET method means retrieve whatever object is identified by the
URI. In the case where the URI refers to a data-producing process,
or a script which can be run by such a process, it is the produced
data which shall be returned as the Object-Body in the response and
not the source text of the script or process (unless that happens
to be the output of the data-producing process).
The semantics of the GET method is changed to a "conditional GET"
if the request message includes an If-Modified-Since header field.
A conditional GET method requests that the identified Object-Body
be transferred only if it has been modified since the date given by
the If-Modified-Since header. If it has been modified (or the
passed If-Modified-Since date is invalid), the response is exactly
the same as for a normal GET. If the object has not been modified
since the If-Modified-Since date, the server shall return a "304
Not Modified" response. The "conditional GET" method is intended to
reduce network usage by allowing cached objects to be refreshed
without requiring multiple requests and transferring unnecessary
data.
Data originating from HTML forms [16] can be passed to the server
using the GET method by appending a "?" and a set of
attribute/value pairs. Section 11.2 describes when to use GET and
POST respectively when passing form data in a request.
5.2.2 HEAD
The HEAD method is identical to GET except that the server must not
return any Object-Body in the response. The metainformation
contained in the HTTP headers in response to a HEAD request should
be identical to the information sent in response to a GET request.
This method can be used for obtaining metainformation about the
object identified by the URI without transferring the Object-Body
itself. This method is often used for testing hypertext links for
validity, accessability, and recent modification.
5.2.3 POST
The POST method is used to request that the origin server accept
the object enclosed in the request as a new subordinate of the
resource identified by the URI in the Request-Line. The POST method
is designed to allow a uniform function to cover the following
functions:
o Annotation of existing documents;
o Posting a message to a bulletin board topic, newsgroup, mailing
list, or similar group of articles;
o Providing a block of data (usually a form) to a data-handling
process, or a script which can be run by such a process;
o Extending a document during authorship.
The posted object is considered to be subordinate to the specified
URI, in the way that a file is subordinate to a directory
containing it, or a news article is subordinate to a newsgroup to
which it is posted.
The client can suggest a URI for identifying the new resource by
including a URI-header field in the request. However, the server
should treat that URI as advisory only and may store the object
under a different URI. The origin server must inform the user agent
of the allocated URI via a URI-header in the response.
The client apply relationships between the new resource and other
existing resources by including Link header fields, as described in
Section 7.14. The server may use the Link information to perform
other operations as a result of the new object being added. For
example, lists and indexes might be updated. However, no mandatory
operation is imposed on the origin server. The origin server may
also generate its own or additional links to other resources.
If a resource has been created on the origin server, the response
should contain the allocated URI and all applicable Link header
fields, along with an Object-Body (preferably of type "text/html")
which describes the status of the request and refers to the new
resource.
A successful POST does not require that the object be created as a
resource on the origin server or made accessible for future
reference. That is, the action performed by the POST method might
not result in a resource that can be identified by a URI. In this
case, a "200 OK" is the appropriate Status-Code returned in the
response. If a resource has been created, "201 Created" should be
the response.
Note: The user agent may not assume any postconditions of
the method in terms of web topology. For example, if a POST
is accepted, the effect may be delayed or overruled by human
moderation, batch processing, etc. The user agent should not
rely on the resource being immediately (or ever) created.
5.2.4 PUT
The PUT method specifies that the enclosed Object in the request is
to be stored under the supplied URI. If the URI points to an
already existing resource, the enclosed Object should be considered
a modified version of the one residing on the origin server. If the
URI does not point to an existing resource, and that URI is capable
of being defined as a new resource from the requesting user agent,
the origin server can create the resource at that URI.
The client can create or modify relationships between the enclosed
Object and other existing resources by including Link header
fields, as described in Section 7.14. As with POST, the server may
use the Link information to perform other operations as a result of
the request. However, no mandatory operation is imposed on the
origin server. The origin server can generate its own or additional
links to other resources.
The actual method for determining how the resource is placed, and
what happens to its predecessor, is defined entirely by the origin
server. If version control is implemented by the origin server, the
Version and Derived-From header fields should be used to help
identify and control revisions to a resource.
5.2.5 DELETE
The DELETE method requests that the origin server delete the
resource identified by the given URI. This method may be overridden
by human interaction (or other means) on the origin server. The
client cannot be guaranteed that the operation has been carried
out, even if the status code returned from the origin server
indicates that the action has been completed successfully. However,
the server should not indicate success unless, at the time the
response is given, it intends to delete the resource.
5.2.6 LINK
The LINK method establishes one or more Link relationships between
the existing resource identified by the URI and other existing
resources. The difference between LINK and other methods allowing
links to be established between the resources is that the LINK
method does not allow any Object-Body to be sent in the request and
does not result in the creation of new resources. The method is
uniquely defined to add metainformation to an existing resource.
5.2.7 UNLINK
The UNLINK method removes one or more Link relationships from the
existing resource identified by the URI. These links may have been
established using LINK, or by any other method supporting the Link
header. The removal of a link to a resource does not imply that the
resource ceases to exist or becomes inaccessible for future
references.
5.3 HTTP-Version
The HTTP-Version element defines the version of the HTTP protocol
being used for the request. If the protocol version is not
specified, the server shall assume that the client uses HTTP
version 0.9 and the response should be formatted as a Simple-
Response.
HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT
Full-Request messages which apply the protocol defined by this
document should use an HTTP-Version of "HTTP/1.0".
5.4 Universal Resource Identifier
The URI is a Universal Resource Identifier, as defined in RFC
1630 [2], and identifies the resource upon which to apply the
request.
URI = <As defined in RFC 1630>
Unless the server is being used as a proxy, a partial URI shall be
given with the assumptions of the protocol (http) and host name
(the server's address) being obvious. That is, if the full URI
looks like
http://info.cern.ch/hypertext/WWW/TheProject.html
then the corresponding partial URI in the Simple-Request or Full-
Request is
/hypertext/WWW/TheProject.html
If the client is sending the request through a proxy, the protocol
and host name must be explicitly declared.
The URI must be encoded using the escaping scheme described in [2].
5.5 Request Header Fields
The request header fields allow the client to pass additional
information about the request (and about the client itself) to the
server. All header fields are optional and conform to the generic
HTTP-header syntax.
Request-Header = User-Agent
| If-Modified-Since
| Pragma
| Authorization
| Proxy-Authorization
| Referer
| From
| Accept
| Accept-Encoding
| Accept-Language
Unknown header fields should be considered Object-Header fields.
5.5.1 User-Agent
The User-Agent field contains information about the user agent
originating the request. This is for statistical purposes, the
tracing of protocol violations, and automated recognition of user
agents for the sake of tailoring responses to avoid particular user
agent limitations or features. Although it is not required, user
agents should always include this field with requests. The field
can contain multiple tokens specifying the product name, with an
optional slash and version designator, and other products which
form a significant part of the user agent. By convention, the
products are listed in order of their significance for identifying
the application.
User-Agent = "User-Agent" ":" 1*( product )
product = token ["/" product-version]
product-version = 1*DIGIT "." 1*DIGIT
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17
Product tokens should be short and to the point -- use of this field
for advertizing or other non-essential information is explicitly
deprecated and will be considered as non-conformance to the
protocol.
Note: Some current proxy applications append their product
information to the list in the User-Agent field. This is no
longer recommended, since it makes machine interpretation of
these fields ambiguous. Instead, proxies should use the
Forwarded header described in Section 4.3.3.
5.5.2 If-Modified-Since
The If-Modified-Since header field is used with the GET method to
make it conditional: if the requested document has not been
modified since the time specified in this field, the document will
not be returned from the server; instead, a "304 Not Modified"
response will be returned without any Object-Body.
If-Modified-Since = "If-Modified-Since" ":" HTTP-date
An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
The purpose of this feature is to allow efficient updates of local
cache information with a minimum amount of transaction overhead.
The same functionality can be obtained, though with much greater
overhead, by issuing a HEAD request and following it with a GET
request if the server indicates that the object has been modified.
5.5.3 Pragma
The Pragma header field is used to specify directives are to be be
applied by servers to which they are relevant (e.g. proxies). They
allow the client to request a certain behavior by all servers along
the length of a request chain. Although multiple pragma directives
can be listed as part of the request, HTTP/1.0 currently only
defines the semantics for the "no-cache" directive.
Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma
extension-pragma = token
When the "no-cache" directive is present, a caching proxy should
not return a document from the cache even though it has not
expired, but it should always request the document from the actual
server.
Pragmas must be passed through by proxies even though they might
have significance to the proxy itself. This is necessary in cases
when the request has to go through many proxies, and the pragma may
affect all of them. It is not possible to specify a pragma for a
specific proxy; however, any pragma-directive not relevant to a
gateway or proxy should be ignored.
5.5.4 Authorization
This version of the HTTP protocol contains a simple access
authentication scheme which is explained in Section 9. The
Authorization header field identifies the user that originated the
request.
Authorization = "Authorization" ":" (
( "Basic" encoded-cookie )
| ( extension-scheme [ extension-encrypted ] ) )
encoded-cookie = <base64 encoding of userid-password>
userid-password = [ token ] ":" *text
extension-scheme = token
extension-encrypted = word
This field is extensible so that it can be used to identify more
advanced encryption schemes. The first word is a specification of
the authorization system in use, followed by an encoded version of
the User-ID and the password (separated by a ":" in decoded form).
The encoding used for the Basic scheme is identical to the base64
encoding of MIME [4] without line breaks. The Basic scheme provides
only a low level of authentication similar to the methods used by
unmodified FTP and Telnet. It cannot be considered a mechanism for
secure transfer.
Note: Since both the User-ID and the password are optional,
the userid-password could be just the single colon character
(":"). However, that is not recommended practice.
5.5.5 Proxy-Authorization
The Proxy-Authorization header field allows the client to identify
itself (or its user) to a proxy which requires authentication. The
format is the same as for Authorization.
Proxy-Authorization
= "Proxy-Authorization" ":" (
( "Basic" encoded-cookie )
| ( extension-scheme [ extension-encrypted ] ) )
Unlike Authorization, the Proxy-Authorization applies only to the
current connection and must not be passed on to higher-level
servers or proxies.
5.5.6 Referer
The Referer field allows the client to specify, for the server's
benefit, the address (URI) of the document (or element within the
document) from which the URI in the request was obtained. This
allows a server to generate lists of back-links to documents, for
interest, logging, optimized caching etc. It also allows obsolete
or mistyped links to be traced for maintenance. The format of the
field is:
Referer = "Referer" ":" URI
Example:
Referer: http://info.cern.ch/hypertext/DataSources/Overview.html
If a partial URI is given, then it should be interpreted relative
to the URI of the object of the request.
Note: Because the source of a link may be considered private
information or may reveal an otherwise secure information
source, it is strongly recommended that the user be able to
select whether or not the Referer field is sent. For
example, a browser client could have a toggle switch for
browsing openly/anonymously, which would respectively
enable/disable the sending of Referer and From information.
5.5.7 From
The From header field, if given, should contain an Internet e-mail
address for the human user who controls the requesting user agent.
It should contain a machine-usable address as defined by addr-spec
in RFC 822:
From = "From" ":" addr-spec
An example is:
From: webmaster@w3.org
This header field may be used for logging purposes and as a means
for identifying the source of invalid or unwanted requests. It
should not be used as an insecure form of access protection. The
interpretation of this field is that the request is being performed
on behalf of the person given, who accepts responsibility for the
method performed. In particular, robot agents should include this
header so that the person responsible for running the robot can be
contacted if problems occur on the receiving end.
The Internet e-mail address in this field does not have to
correspond to the Internet host which issued the request. (For
example, when a request is passed through a proxy, then the
original issuer's address should be used). The address should, if
possible, be a valid Internet e-mail address, whether or not it is
in fact an Internet e-mail address or the Internet e-mail
representation of an address on some other mail system.
Note: The client should not send the From header field
without the user's approval, as it may conflict with the
user's privacy interests or their site's security policy. It
is strongly recommended that the user be able to disable,
enable, and modify the value of this field at any time prior
to a request.
5.5.8 Accept
The Accept header field can contain a list of media types which are
acceptable as a response to the request. The set given by the
client should represent what is acceptable given the context of the
request.
The field may be folded onto several lines and more than one
occurrence of the field is allowed (with the semantics being the
same as if all the entries had been in one field value).
Accept = "Accept" ":" 1#(
("*" | type) "/" ("*" | subtype)
*(";" parameter)
[ ";" "q" "=" ( "0" | "1" | float ) ]
[ ";" "mxb" "=" 1*DIGIT ] )
float = <ANSI-C floating point text representation,
where (0.0 < float < 1.0)>
q is the quality factor of how well the client can handle the media
type and mxb is the maximum accepted size of the Object-Body in
number of octets (decimal). The definition does not prohibit
duplicate accept-param's, but leaves the interpretation undefined.
See Section 8 for a description of the negotiation algorithm. If at
least one Accept header is present, a quality factor of 0 is
equivalent to not sending an accept header field containing that
media-type or set of media-types. The default values are: q=1 and
mxb=undefined (i.e. infinity).
In order to save time, and also allow clients to receive media
types of which they may not be aware, an asterisk "*" may be used
in place of either the type token and/or the subtype token. The
example
Accept: audio/*; q=0.2, audio/basic
should verbally be interpreted as "if you have audio/basic, send
it; otherwise send me some other audio".
If no Accept header is present, then it is assumed that the client
accepts all formats with quality factor 1. This is equivalent to
the client sending the following accept header field:
Accept: */*; q=1
or
Accept: */*
A more elaborate example is
Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8; mxb=100000, text/x-c
Verbally, this should be interpreted as "text/html and text/x-c are
the preferred media types, but if they do not exist then send the
Object-Body in text/x-dvi if the object is less than 100000 bytes.
If this is not the case then send text/plain".
Note: In earlier versions of this document, the mxs
parameter defined the maximum acceptable delay in seconds
before the response would arrive. This has been removed as
the server has no means of obtaining a useful reference
value. However, this does not prevent the client from
internally measuring the response time and optimizing the
accept header field accordingly.
5.5.9 Accept-Encoding
The Accept-Encoding header field is similar to Accept, but lists
the Content-Encoding types which are acceptable in the response.
Content-Encoding is described in Section 7.4.
Accept-Encoding = "Accept-Encoding" ":"
1#(encoding-mechanism [ ";" encoding-param ] )
encoding-mechanism = extension-encoding
encoding-param = "q" "=" ( "0" | "1" | float )
extension-encoding = token
q is the quality factor of how well the client can handle the
encoding type. The default value is q=1. As no encoding-mechanism's
have been registered by IANA [15], all values are of type extension-
encoding. However, two well-known extension-encoding's are:
"x-compress", "x-gzip"
If no Accept-Encoding is present then it is assumed that the client
accepts no encoding at all. An example of use is
Accept-Encoding: x-compress
5.5.10 Accept-Language
The Accept-Language header field is similar to Accept, but lists
the set of natural languages acceptable for the response to the
request.
Accept-Language = "Accept-Language" ":"
1#(language-dialect *1(";" language-param) )
language-dialect = ("*" | language) ["/" dialect ]
language-param = "q" "=" ( "0" | "1" | float)
language = <As defined in ISO 639 but case-insensitive>
dialect = <As defined in ISO 3166 but case-insensitive>
As with the Accept field, a quality factor q can be specified which
in this case describe the level of intelligibility to the user. The
default value is q=1. The definition does not prohibit duplicate
language-param's, but leaves the interpretation undefined. An
example of it's use is
Accept-Language: dk, en/gb; q=0.5
meaning: "Send me a Danish version if you have it; else a British
English version."
If no Accept-Language is present, it is assumed that the client
accepts all natural languages with quality factor 1.
If the server cannot service the request with the language
specified, or if the languages specified only represent a subset in
case of a multi-linguistic Object-Body, it is not illegal to serve
the request in an unspecified language. The character "*" can be
used to indicate "any language" and/or "any dialect".
Note: As intelligibility is highly dependent on the
individual user, it is recommended that client applications
make the choice of linguistic preference available to the
user.
6. Response
If the client has issued an HTTP request, the response from the
server shall consist of the following:
Response = Simple-Response | Full-Response
Simple-Response= [Object-Body]
Full-Response = Status-Line ; see Section 6.1
*General-Header ; see Section 4.3
*Response-Header ; see Section 6.4
*Object-Header ; see Section 7
CRLF
[ Object-Body ] ; see Section 3.2
A Simple-Response should only be sent in response to an HTTP/0.9
Simple-Request. Note that the Simple-Response consists only of the
object that was requested and is terminated by the server closing
the connection.
6.1 Status-Line
The Status-Line consists of the protocol version followed by a
numeric status code and its associated textual phrase, with each
element separated by SP characters. No CR or LF is allowed except
in the final CRLF sequence.
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
6.2 HTTP Version
The HTTP-Version element identifies the protocol version being used
by the server. The format of this field is identical to the
corresponding HTTP-Version field in the Request-Line described in
Section 5.3.
6.3 Status Codes and Reason Phrases
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. The Reason-Phrase is
intended to give a short textual description of the Status-Code.
The Status-Code is intended for use by automata and the Reason-
Phrase is intended for the human user. The client is not required
to examine the Reason-Phrase, nor to pass it on to the human user.
Status-Code = 3DIGIT
Reason-Phrase = token *( SP token )
All responses, regardless of the Status-Code, may contain an Object-
Header and/or an Object-Body. This can either be the object pointed
to by the requested URI or an object containing further explanation
of the Status-Code. In the latter case, the preferred media type is
"text/html", but "text/plain" is also acceptable.
The first digit of the Status-Code defines the class of responses
known to HTTP. The last two digits do not have any categorization
role. There are 5 values for the first digit:
o 1xx: Not used, but reserved for future use
o 2xx: Success - The requested action was successfully received
and understood
o 3xx: Redirection - Further action must be taken in order to
complete the request
o 4xx: Client Error - The request contains bad syntax or is
inherently impossible to fulfill
o 5xx: Server Error - The server could not fulfill the request
The values of the numeric status codes and an example set of
corresponding Reason-Phrase's are presented below. Every Status-
Code has a description of which method it can follow and any
metainformation required in the HTTP-header.
6.3.1 Successful 2xx
This class of status codes indicates that the client's request was
successfully received and understood.
200 OK
o Following: GET, HEAD, POST
o Required metainformation: none
The request could be fulfilled and an Object-Header should be
returned to the client in the response. In the case of GET, the
response should also contain an Object-Body.
201 Created
o Following: POST, PUT
o Required metainformation: URI-header
This indicates that the POST has been successful or that the PUT
resulted in a new object. The newly created object can be
referenced by the URI returned in the URI-header field in the
response. This action can, at any time, be overridden at the origin
server (possibly by human intervention), so this status code is no
guarantee that the object continue to be available at the given URI.
202 Accepted
o Following: GET, HEAD, PUT, POST, DELETE
o Required metainformation: none
The request has been accepted for processing, but the processing
has not been completed. The request may or may not eventually be
acted upon, as it may be disallowed when processing actually takes
place. There is no facility for re-sending a status code from an
asynchronous operations such as this.
203 Provisional Information
o Following: GET, HEAD, POST
o Required metainformation: none
When received in the response, this indicates that the returned
metainformation in the HTTP-header is not the definitive set as
available from the origin server, but is gathered from a local or a
third party copy. The set presented can either be a subset or a
superset of the original version, for example including annotation
information about the resource.
204 No Response
o Following: GET, HEAD, POST
o Required metainformation: none
The server has received the request but there is no information to
send back, and the client should stay in the same document view.
This is mainly to allow input for scripts without changing the
document at the same time.
205 Deleted
o Following: DELETE
o Required metainformation: none
The DELETE method was successful and the object has been removed by
the requested server. This action can at any time be overridden by
the origin server, for example by human interaction, so this status
code is no guarantee that the operation has in fact been carried
out.
206 Modified
o Following: PUT
o Required metainformation: none
The PUT method was successful and the object has been modified on
the requested server. This action can at any time be overridden at
the origin server, for example by human interaction so this status
code is no guarantee that the operation has in fact been carried
out.
6.3.2 Redirection 3xx
This class of status codes indicates that further action needs to
be taken by the client in order to fulfill the request. The action
required can normally be carried out by the client without
interaction with the user, but it is strongly recommended that this
only takes place if the method used in the request is either GET or
HEAD.
301 Moved Permanently
o Following: GET, HEAD, POST, PUT
o Required metainformation: URI-header, Location
The object requested has been assigned a new permanent URI, and any
future references to this object must be done using the returned
URI. Clients with link editing capabilities are encouraged to
automatically relink references to the URI requested to the new
reference returned by the server, where possible.
Note: It is possible for the server to send back this status
code in response to a request using the PUT and POST
methods. However, as this might change the conditions under
which the request was issued, the user agent should not
automatically redirect the request unless it can be
confirmed by the user.
302 Moved Temporarily
o Following: GET, HEAD, POST, PUT
o Required metainformation: URI-header, Location
The data requested resides temporarily under a different URI. As
the redirection may be altered on occasion, the client should on
future requests from the user continue to use the original URI used
for this request and not the URI returned in the URI-header field.
Note: It is possible for the server to send back this status
code in response to a request using the PUT and POST
methods. However, as this might change the conditions under
which the request was issued, the user agent should not
automatically redirect the request unless it can be
confirmed by the user.
303 Method
o Required metainformation: none
This code is obsolete.
304 Not Modified
o Following: conditional GET
o Required metainformation: none
If the client has performed a conditional GET request and access is
allowed, but the document has not been modified since the date and
time specified in the If-Modified-Since field, the server shall
respond with this status code and must not send the Object-Body to
the client. Metainformation contained in the response should only
contain information relevant to cache managers and which may have
changed independently of the object's Last-Modified date. Examples
of relevant header fields are: Date, Server, and Expires. However,
none of them are mandatory.
6.3.3 Client Error 4xx
The 4xx class of status codes is intended for cases in which the
client seems to have erred. The codes can follow any method
described in Section 5.2, and the set consists of:
400 Bad Request
o Required metainformation: none
The request had bad syntax or was inherently impossible to be
satisfied. The client is discouraged from repeating the request
without modifications.
401 Unauthorized
o Required metainformation: WWW-Authenticate
The server must return a WWW-Authenticate header field as described
in Section 6.4.2 containing a list of authorization schemes in
which at least one must be fulfilled in order for the client to
obtain the Object-Body. The client should then retry the request
with a suitable Authorization header field. The HTTP access
authentication scheme is explained in Section 9.
402 Payment Required
o Required metainformation: none
This code is not currently supported, but is reserved for future
use.
403 Forbidden
o Required metainformation: none
The request is, for some reason unknown to the client, forbidden.
Authorization will not help and the request should not be repeated.
This status code can also be used if the server does not want to
make public whether the request can not be fulfilled due to
insufficient authorization from the client or because the object
does not exist.
404 Not Found
o Required metainformation: none
The server has not found anything matching the URI given. No
indication is given whether the condition is temporary or permanent.
405 Method Not Allowed
o Required metainformation: Allow
The method specified in the Request-Line is not allowed for the
object identified by the URI. The server should send back an Allow
header containing a list of valid method's as explained in Section
7.1.
406 None Acceptable
o Required metainformation: Content-Type, Content-Encoding,
Content-Language
The server has found an object matching the URI given, but not one
that matches all of the conditions identified in the Accept, Accept-
Encoding, and Accept-Language request headers. The response should
include at least the Content-Type, the Content-Encoding, and the
Content-Language, but is encouraged to include the object's
complete metainformation. No Object-Body can be included in the
response.
407 Proxy Authentication Required
o Required metainformation: Proxy-Authenticate
This code is similar to "401 Unauthorized" but it indicates that
the user agent must first authenticate itself with the proxy. The
proxy must return a Proxy-Authenticate header field as described in
Section 6.4.3 containing a list of authorization schemes in which
at least one must be fulfilled in order for the client to use the
proxy. The client should then create a new request with the proxy
as the server destination and with a suitable Proxy-Authorization
header field. The HTTP access authentication scheme is explained in
Section 9.
408 Request Timeout
o Required metainformation: none
This code indicates that the client did not produce a request
within a time that the server was prepared to wait. If the client
is still actively generating the request, it should immediately
stop sending further information to the server.
6.3.4 Server Errors 5xx
Response status codes beginning with the digit "5" indicate cases
in which the server is aware that it has erred or is incapable of
performing the request. These codes can follow any method at any
time.
Note: For all of the 5xx codes, the server is encouraged to
send back an HTTP-header and an Object-Body containing an
explanation of the error situation, and whether it is a
temporary or permanent condition.
500 Internal Server Error
The server encountered an unexpected condition which prevented it
from fulfilling the request.
501 Not Implemented
The server does not support the functionality required to fulfil
the request.
502 Bad Gateway
This is equivalent to "500 Internal Server Error", but for the case
of a gateway or proxy accessing some other service, this indicates
that the response from the other service was invalid. As from the
point of view of the client and the HTTP transaction, the other
service is hidden within the gateway or proxy, this may be treated
identically to "500 Internal Server Error", but has more diagnostic
value.
503 Service Unavailable
o Required metainformation: Retry-After
The server is currently unable to handle the request. This can
either be due to overload of the server or servicing of the server.
The implication is that this is a temporary condition which will be
alleviated after a delay indicated in the Retry-After header. If no
Retry-After is present in the response then the client should
handle the response as identical to a "500 Internal Server Error".
504 Gateway Timeout
This is equivalent to "500 Internal Server Error", but for the case
of a gateway or proxy accessing some other service, this indicates
that the response from the other service did not return within a
time that the gateway was prepared to wait. As from the point of
view of the client and the HTTP transaction, the other service is
hidden within the gateway or proxy, this may be treated identically
to "500 Internal Server Error", but has more diagnostic value.
6.4 Response Header Fields
The response header fields allow the server to pass additional
information about the response which cannot be placed in the Status-
Line. These header fields are not intended to give information
about an Object-Body returned in the response, but about the server
itself.
Response-Header= Server
| WWW-Authenticate
| Proxy-Authenticate
| Retry-After
Unknown header fields should be considered Object-Header fields.
6.4.1 Server
The Server header field contains information about the software
being used by the origin server program handling the request. The
field is analogous to the User-Agent field and has the following
format:
Server = "Server" ":" 1*( product )
Example:
Server: CERN/3.0 libwww/2.17
If the response is being forwarded through a proxy, the proxy
application must not add its data to the product list. Instead, it
should include a Forwarded field, as described in Section 4.3.3.
6.4.2 WWW-Authenticate
The WWW-Authenticate header field must be included as part of the
response if the server sends back a "401 Unauthorized" Status-Code
on a request from the client as part of the Basic Authentication
Scheme described in Section 9. This header field indicates the
authentication scheme in use and the realm in which the requested
URI belongs.
WWW-Authenticate = "WWW-Authenticate" ":" (
( "Basic" realm )
| ( extension-scheme realm ) )
realm = "Realm" "=" 1#( "<" URI ">" )
The first word of the field value identifies the authorization
scheme in use and is followed by the realm of the protected URI.
The realm is a comma separated list of URIs, where relative URLs
should be interpreted relative to the URI of the requested resource
in the RequestLine. If a request is authenticated and a realm
specified, the User-ID and password should be valid for all other
requests within this realm.
Note: The realm may span more than one origin server.
6.4.3 Proxy-Authenticate
The Proxy-Authenticate header field must be included as part of the
response if the proxy sends back a "407 Proxy Authentication
Required" Status-Code on a request from the client. This header
field indicates the authentication scheme in use and the realm for
which the proxy is protected.
Proxy-Authenticate = "Proxy-Authenticate" ":" (
( "Basic" realm )
| ( extension-scheme realm )
Unlike WWW-Authenticate, the Proxy-Authenticate applies only to the
current connection and must not be passed on to lower-level user
agents or proxies.
6.4.4 Retry-After
The Retry-After header field can be used with "503 Service
Unavailable" to indicate how long the service is expected to be
unavailable to the requesting client. The value of this field can
be either an absolute HTTP-date or an integer number of seconds (in
decimal) after the time of the response.
Retry-After = "Retry-After" ":" ( HTTP-date | delta-seconds )
delta-seconds = 1*DIGIT
Two examples of use are
Retry-After: Wed, 14 Dec 1994 18:22:54 GMT
Retry-After: 120
In the latter example, the delay is 2 minutes.
7. Object Header Fields
Full-Request and Full-Response messages can contain Object-Header
fields and an Object-Body (as defined in Section 3). This section
specifies the format and contents of the Object-Header fields.
Object-Header fields define metainformation about the Object-Body.
All are optional.
Object-Header = Allow
| Content-Length
| Content-Type
| Content-Encoding
| Content-Transfer-Encoding
| Content-Language
| Expires
| Last-Modified
| URI-header
| Location
| Version
| Derived-From
| Title
| Link
| extension-header
extension-header=HTTP-header
In this section, recipient refers to either the client or the
server, depending on who receives the object. Each object header
field is explained in the subsections below. Other header fields
are allowed but cannot be assumed to be recognizable by the
recipient. Unknown header fields should be ignored by the
recipient, but passed on to downstream recipients (if any).
7.1 Allow
The "Allow" header field lists the set of methods supported by the
object identified by the requested URI. The purpose of this field
is strictly to inform the recipient of valid methods associated
with the object. This does not prevent a client from trying other
methods. However, it is recommended that the indications given by
this field be followed. This field has no default value. If left
undefined, the set of allowed methods is defined by the origin
server at the time of each request.
Allow = "Allow" ":" 1#method
Example of use:
Allow: GET, HEAD, PUT
Note: If a response passes through a proxy which does not
understand one or more of the methods indicated in the Allow
header, the proxy should not try to modify the Allow header,
since the user agent may have other means of communicating
with the origin server.
7.2 Content-Length
The Content-Length header field indicates the size of the Object-
Body (in decimal number of octets) sent to the recipient or, in the
case of the HEAD method, the size of the Object-Body that would
have been sent had the request been a GET.
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Even though it is not mandatory, applications are strongly
encouraged to use this field to indicate the size of the Object-
Body to be transferred regardless of the media type of the object.
Any Content-Length of size greater than or equal to zero is a valid
value. If undefined, the length of the Object-Body may be
determined by the media type (if a multipart type is used), by the
content encoding (if a delimited encoding is used), or by the
closing of the connection by the server. However, since many
applications do not accept multipart types or delimited encodings,
a valid Content-Length is generally required for objects contained
in PUT and POST requests.
Note: The meaning of this field is significantly different
from the corresponding specification in MIME, where it is an
optional field used within the "message/external-body"
Content-Type. In HTTP, it should be used whenever the
object's length can be determined prior to being transferred.
7.3 Content-Type
The Content-Type header field indicates the Internet media type of
the Object-Body (as described in Section 4.2) sent to the recipient
or, in the case of the HEAD method, the media type that would have
been sent had the request been a GET.
Content-Type = "Content-Type" ":" media-type
An example of the field is
Content-Type: text/html; charset=ISO-8859-1
All media-type's registered by IANA should be preferred over
extension tokens. However, HTTP does not limit conforming
applications to the use of officially registered media types, nor
does it encourage the use of an "x-" prefix for unofficial types
outside of explicitly short experimental use between consenting
applications. Data providers are strongly encouraged to register
their media types with IANA via the procedures outlined in RFC
1590 [13].
The Content-Type header field has no default value. If and only if
the media type is unknown, the receiver may attempt to guess the
media type via inspection of its content and/or the filename
extension(s) of the URL used to access the object. If the media
type remains unknown, the receiver should treat it as type
"application/octet-stream".
7.4 Content-Encoding
The Content-Encoding header field, unique to HTTP, is used as a
modifier to the media-type. When present, its value indicates the
encoding mechanism applied to the associated Object-Body prior to
it being enclosed in the message, and thus what decoding mechanism
must be applied in order to obtain the media-type referenced by the
Content-Type header field. This is primarily used to allow object
compression without losing the identity of the underlying media
type.
Content-Encoding = "Content-Encoding" ":" encoding-mechanism
An example of its use is
Content-Encoding: x-gzip
This field should not be confused with the Content-Transfer-
Encoding field defined below. The purpose of the Content-Transfer-
Encoding is "to indicate the type of transformation that has been
used in order to represent the object in an acceptable manner for
transport." In contrast, Content-Encoding is used to indicate any
form of compression, encryption, or packetization mechanism used to
transform the data prior to being transported, such that it is in a
more convenient form for storage and/or transport. The result after
encoding is usually binary, but could be any type defined by the
Content-Transfer-Encoding field.
7.5 Content-Transfer-Encoding
Because all HTTP communication takes place on an 8-bit clean
connection, the default Content-Transfer-Encoding for all messages
is "binary". Note that this differs from the required default in
MIME [4], so gateways between HTTP and MIME-compliant protocols
must add an explicit "Content-Transfer-Encoding: binary" to the
message header if a Content-Transfer-Encoding is not already
present.
Content-Transfer-Encoding = "Content-Transfer-Encoding" ":"
cte-mechanism
cte-mechanism = token
7.6 Content-Language
The Content-Language field describes the natural language of the
Object-Body. It is defined as:
Content-Language = "Content-Language" ":" 1#lang-dia
lang-dia = language ["/" dialect ]
An example of its use is
Content-Language: dk
means that the content of the message is in Danish with no dialect
specified. The example
Content-Language: en/gb, dk
means that the language is Danish and British English.
Multilinguistic Object-Body's can be described using a list of lang-
dia codes. This document does not specify any means to indicate the
extent to which different natural languages are represented in the
Object-Body.
Note: This field can be defined not only for textual
documents, but also for audio and possibly other media as
well. It should not be considered limited to Object-Body's
of type "text/*".
In the absence of an explicit Content-Language header, the client
should make no assumptions about the language of the returned
Object-Body, as it might be a language-neutral or a multilingual
document.
7.7 Expires
The Expires field gives the date and time after which the
information given ceases to be valid and should be retrieved again
if it has been kept as a local copy. This allows control of caching
mechanisms, but the date and time indicated does not necessarily
imply that the original object will cease to exist. This is
completely controlled by the server. The format is an absolute date
and time as defined by HTTP-date in Section 4.1. The formal
description is
Expires = "Expires" ":" HTTP-date
and an example of the use is
Expires: Thu, 01 Dec 1994 16:00:00 GMT
Note: This field can also be used for automatic refreshing
of dynamic or volatile data. However, this is completely
dependent on the implementation of the client application to
automatically issue a new request when the object has
expired.
Object's generated by data-producing processes, or scripts which
can be run by such processes, are often dynamic by nature.
Therefore, it is strongly recommended that responses containing
such Objects's contain an Expires header field.
7.8 Last-Modified
The Last-Modified header field indicates the date and time at which
the sender believes the object was last modified. The exact
semantics of this field are defined in terms of how the receiver
should interpret it: If the receiver has a copy of this object
which is older than the date given by the Last-Modified field, that
copy should be considered stale.
Last-Modified = "Last-Modified" ":" HTTP-date
An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
The exact meaning of this header field depends on the
implementation of the sender. For files, it may be just the file
system last-mod date. For entities with dynamically included parts,
it may be the most recent of the set of last-mod dates of its
component parts. For database gateways, it may be the last-update
timestamp of the record. For virtual objects, it may be the last
time its internal state changed. In any case, the recipient should
only know (and care) about the result -- whatever gets stuck in the
Last-modified: header -- and not worry about how it was obtained.
7.9 URI Header
The URI-header field contains a URI by which the object may be
found. It should not be confused with the token in the Request-Line
described in Section 5.4. As for a normal request, there is no
guarantee that the resource can be accessed using the URI
specified. The field is normally a part of a response having Status-
Code "301 Moved Permanently" or "302 Moved Temporarily".
URI-header = "URI" ":" 1#( "<" URI ">" [ ";" vary ] )
vary = "vary" "=" <"> 1#vary-param <">
vary-param = "type" | "language" | "version" | "encoding"
| "user-agent" | extension-vary
extension-vary = token
All URI's specified in this field can be either absolute or
relative to the URI given in the RequestLine as specified by [9].
If a URI refers to a set of variants, then the dimensions in which
the variants differ must be given with the vary parameters.
Multiple occurrences of vary-param in the vary field give
alternative access names or addresses for the object. An example of
the field is:
URI: <http://info.cern.ch/hypertext/WWW/TheProject.multi>;
vary="type,language"
This indicates that the URI indicated covers a group of possible
resources which varies in media type and in natural language. The
client can specify which of these objects to be returned in the
response to a request using the request header fields: Accept,
Accept-Encoding, Accept-Language, and Version. Another example is:
URI: <http://info.cern.ch/hypertext/WWW/TheProject.ps>;
vary="encoding"
This indicates that the resource pointed to by the URI exists in
different encodings as defined by the Content-Encoding field.
7.10 Location
The Location header field is an earlier form of the URI-header and
is considered obsolete. However, HTTP/1.0 clients and servers
should continue to support the Location header in order to properly
interface with older applications. The purpose of Location is
identical to that of the URI-header, except that no variants can be
specified and only one absolute location URI is allowed.
Location = "Location" ":" URI
An example is
Location: http://info.cern.ch/hypertext/WWW/NewLocation.html
7.11 Version
The Version field defines a version number referring to the current
contents of an evolving object resident on the origin server.
Together with the Derived-From field described in Section 7.12, it
allows groups of people to work simultaneously on the creation of a
work as an iterative process. The field should be used to indicate
evolution along a single path of a particular work. It should not
be used to indicate derived works or renditions in different
representations.
Version = "Version" ":" *text
Note: The field should be present in the response if PUT is
an allowed method to perform on the object pointed to by the
requested URI. However the presence of the field can not be
taken as an indication whether PUT is allowed or not.
7.12 Derived-From
The Derived-From field contains the most recent value of the
Version field before any modifications local to the transmitting
application have been carried out on an evolving resource. The
definition of the field value must be identical to the Version
field value.
Derived-From = "Derived-From" ":" *text
The definition of this field allows both the server and the client
to employ a code management system to merge different versions of
an evolving resource. As for the Version field, the Derived-From
may only be used to indicate evolution along a single path of a
particular work. It should not be used to indicate derived works or
renditions in different representations.
Note: The definition allows different code management
systems to be employed by the involved parties. The only
requirement is a conforming mapping between any internal
versioning system and the one defined by Derived-From and
Version.
7.13 Title
This header field indicates the title of the document, which is not
to be considered as part of the object. The definition of the field
is:
Title = "Title" ":" *text
The field differs from the "Subject" field described in RFC 822 in
that title is defined by the creator/author of a resource, but the
"Subject" field is defined by the originator. The field is to be
considered isomorphic with the <TITLE> element in HTML [16].
7.14 Link
The Link header provides a means for describing the relationship
between HTTP-Object's. An object can have multiple Link elements
and can typically indicate relationships like hierarchical
structure. The field is semantically equivalent to the <LINK>
element in an HTML document.
Link = "Link" ":" 1#("<" URI ">" [ ";" "REL" "=" relation ] )
relation = "UseIndex" | "UseGlossary" | "Contents"
| "Next" | "Previous" | "Parent"
| "BookMark" | "Made" | "Help"
The reader is referred to the HTML specification [16] for a full
explanation of the semantics for LINK relationships. Examples of
usage include:
Link: <http://info.cern.ch/previous>; REL="Previous"
Link: <mailto:timbl@info.cern.ch>; REL="Made"
The first example indicates that this object is logically a
continuation of the previous object identified by the URI. The
second indicates that the author of the object is identified by the
given e-mail address.
Note: It has been proposed that any HTML metainformation
element (allowed within the <HEAD> as opposed to <BODY>
element of the document) be a valid candidate for an HTTP
object header. This document defines the two header fields
Link and Title which both are examples of this.
8. HTTP Negotiation Algorithm
The goal of the negotiation algorithm is to map a set of parameters
into a one-dimensional space where the calculated weights represent
the "degradation" figure of the resource. The maximum value of this
set represents the media-type in which the Object-Body optimally
should be returned to the client.
It is assumed that it is possible to assign an absolute value
representing the amount of loss of value when the Object-Body is
rendered into a specific media type. Whilst this is a very
subjective measurement, and in fact largely a function of the
document in question, the approximation is made that one can define
this degradation figure as a function of merely the representation
involved.
It is furthermore assumed that the cost to the user of viewing an
Object also is a function of the time taken for the presentation.
We first assume that the cost is linear in time, and then assume
that the time is linear in the size of the Object-Body.
The calculated weights are normalized to a real number between 0
and 1 where 0 is the minimum value and 1 is the maximum value. This
document defines the following parameters to be included in the
algorithm:
q The quality factor representing the level of degradation when
rendering the Object-Body in a specific media-type in the
client application. The value is normalized so that q OE[0,1],
where the default value is q=1.
qs Equivalent to the q factor but for the server application in
case it can perform media-type conversions. The default value
is qs=1.
mxb The maximum number of bytes in the Object-Body accepted by the
client. The default value is mxb=undefined (i.e. infinity).
bs The actual number of bytes of the Object-Body as a function of
media-type and encoding-mechanism. This value equals the value
send in the Content-Length field. The default value is bs=0.
The discrete mapping function is defined as:
{ if mxb=undefined, then (qs * q) }
Q(q,qs,mxb,bs) = { if mxb >= bs, then (qs * q) }
{ if mxb < bs, then 0 }
The maximum of the Q function represents the preferred media-type
to be used for transmitting the Object-Body to the client.
Use of content variants and/or this particular negotiation algorthm
is not mandatory. However, it is strongly recommended as it can
save a significant amount of bandwidth. The hope is that fine
decisions will not have to be made, since in most cases the results
for different formats will be differ widely, and there will be a
clear winner.
Note: The algorithm described does not take into account the
cost of any conversion performed by a gateway or proxy.
Although this is an important topic, it is considered more
important to maintain any gateways or proxy as transparent
parties in the transmission between the client and the
server.
9. Basic Access Authentication Scheme
The basic authentication scheme described here is to be considered
a non-secure way of filtering unauthorized access to resources on
an HTTP server. It is based on the assumption that the connection
between the client and the server can be regarded as a trusted
carrier. As this is not generally true on an open network, the
basic access authentication scheme should be used accordingly. In
spite of this, clients are strongly encouraged to implement the
scheme in order to communicate with servers that use it.
The basic authentication scheme is based on the model that the
client must authenticate itself using a user-ID and a password as a
function of the origin server, and the realm on that server. The
server will service the request only if it can validate the user-ID
and password in the realm where the resource identified by the URI
is located. The protected resources on the server can be divided
into a set of realms which can use different password files, so
that different realms can be accessible by different users.
A typical example of an authenticated request has one of the
following two profiles:
o The client requests a document without sending an Authorization
header field
o The server responds with a "401 Unauthorized" status code as
described in Section 6.3.3 and an WWW-Authenticate header field
o The client knows already a valid user-ID and a password for the
realm indicated by the WWW-Authenticate header field or it
prompts the user.
o The clients generates a new request with an Authorization
header field
o The server replies by sending the requested Object to the
client.
In this example, the client has no authorization information prior
to the initial request. In the next example, the client does have
such information due to a previous request within the realm
indicated by the server. The example would then look like:
o The client requests a document with an Authorization header
field
o The server replies by sending the requested Object to the
client.
This specification of the HTTP protocol allows other authentication
schemes to be implemented using either the same frame as the basic
scheme or additional header fields. However, these can not be
assumed to be generally accepted by applications conforming to this
specification.
The client is encouraged to only use the second approach after it
has verified that the requested URI is pointing to a resource
within the realm where the content of the authorization header
field is valid for accessing the URI. If no realm has been
indicated then the second approach should be used only when the
realm is known from previous requests.
As described in Section 1.2, this specification does not require
that the connection be closed after each request. However, when
HTTP is used on top of TCP, it is recommended that the connection
be closed between the first and second client request in an
authenticated request.
Proxies must be completely transparent in the basic access
authentication scheme. That is, they must forward the
WWW-Authenticate and Authorization headers untouched. If a proxy
wants to authenticate a client before a request is forwarded to
the server, it can be done using the Proxy-Authenticate and
Proxy-Authorization headers.
10. Registration Authority
The HTTP Registration Authority is responsible for maintaining
lists of:
o Authorization schemes (as described in Section 9)
o Common method semantics for a HTTP request and response
o Data format names (as MIME Content-Types or Internet Media
Types)
o Data encoding names (as MIME Content-Encoding)
It is proposed that the Internet Assigned Numbers Authority [15] or
their successors take this role.
11. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.0 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
11.1 Authentication of Clients
As mentioned in Section 9, the Basic Authentication scheme used in
HTTP/1.0 is not considered to be a secure method of user
authentication, nor does it prevent the Object-Body from being
transmitted in clear text across the physical network used as the
carrier. The protocol does allow for additional authentication
schemes and encryption mechanisms to be employed to increase the
security level.
11.2 Idempotent Methods
The writers of client software should be aware that the software
represents the user in their interactions over the net, and should
be careful to allow the user to be aware of any actions they may
take which may have an unexpected significance to themselves or
others.
In particular, the convention has been established that the GET and
HEAD methods should never have the significance of taking an
action. The link "click here to subscribe"--causing the reading of a
special "magic" document--is open to abuse by others making a link
"click here to see a pretty picture". These methods should be
considered "safe" and should not have side effects. This allows the
client software to represent other methods (such as POST, PUT and
DELETE) in a special way, so that the user is aware of the fact
that an action is being requested.
11.3 Abuse of Server Log Information
A server is in the position to save personal data about information
requested by readers. This information is clearly confidential in
nature and its handling may be constrained by law in certain
countries. Server providers shall ensure that such material is not
distributed without the permission of any individuals that are
identifiable by the published results.
Two header fields are worth special mention in this context:
Referer and From. The Referer field allows reading patterns to be
studied and reverse links drawn. Although it can be very useful,
its power can be abused if user details are not separated from the
information contained in the Referer. Even when the personal
information has been removed, the Referer field may have indicated
a secure document's URI, whose revelation would itself be a breach
of security.
The information sent in the From field might conflict with the
user's privacy interests or their site's security policy, and hence
it should not be transmitted without the user being able to
disable, enable, and modify the contents of the field prior to a
request.
12. Acknowledgments
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for RFC 822 [7]. Similarly,
it reuses the Content-Type definitions provided by Nathaniel
Borenstein and Ned Freed for MIME [4]. We hope that their inclusion
in this specification will help reduce past confusion over the
relationship between HTTP/1.0 and Internet mail.
The HTTP protocol has evolved considerably over the past three
years. It has benefited from a large and active developer community--
the many people who have participated on the www-talk mailing list--
and it is that community which has been most responsible for the
success of HTTP and of the World-Wide Web in general. Marc
Andreessen, Dan Connolly, Ari Luotonen, Rob McCool, Dave Raggett,
Tony Sanders, and Marc VanHeningen deserve special recognition for
their efforts in defining aspects of the protocol for early
versions of this specification. Bob Denny assisted in proof-reading
the specification and performing sanity-checks as it was being
rewritten.
13. References
[1] F. Anklesaria, M. McCahill, P. Lindner, D. Johnson, D. Torrey,
and B. Alberti. "The Internet Gopher Protocol: A distributed
document search and retrieval protocol." RFC 1436, University
of Minnesota, <URL:http://ds.internic.net/rfc/rfc1436.txt>,
March 1993.
[2] T. Berners-Lee. "Universal Resource Identifiers in WWW: A
Unifying Syntax for the Expression of Names and Addresses of
Objects on the Network as used in the World-Wide Web." RFC
1630, CERN, <URL:http://ds.internic.net/rfc/rfc1630.txt>,
June 1994.
[3] T. Berners-Lee, L. Masinter, and M. McCahill. "Uniform Resource
Locators (URL)." Internet-Draft (work in progress), CERN, Xerox
PARC, University of Minnesota, <URI:http://ds.internic.net/
internet-drafts/draft-ietf-uri-url-08.txt>, October 1994.
[4] N. Borenstein and N. Freed. "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing
the Format of Internet Message Bodies." RFC 1521, Bellcore,
Innosoft, <URL:http://ds.internic.net/rfc/rfc1521.ps>,
September 1993.
[5] K. Moore. "MIME (Multipurpose Internet Mail Extensions) Part
Two: Message Header Extensions for Non-ASCII Text." RFC 1522,
University of Tennessee,
<URL:http://ds.internic.net/rfc/rfc1522.txt>, September 1993.
[6] R. Braden. "Requirements for Internet hosts - application and
support." STD 3, RFC 1123, IETF,
<URL:http://ds.internic.net/rfc/rfc1123.txt>, October 1989.
[7] D. H. Crocker. "Standard for the Format of ARPA Internet Text
Messages." STD 11, RFC 822, UDEL,
<URL:http://ds.internic.net/rfc/rfc822.txt>, August 1982.
[8] F. Davis, B. Kahle, H. Morris, J. Salem, T. Shen, R. Wang,
J. Sui, and M. Grinbaum. "WAIS Interface Protocol Prototype
Functional Specification." (v1.5), Thinking Machines Corp.,
<URL:ftp://quake.think.com/pub/wais/doc/protspec.txt>,
April 1990.
[9] R. T. Fielding. "Relative Uniform Resource Locators."
Internet-Draft (work in progress), UC Irvine,
<URL:http://ds.internic.net/internet-drafts/
draft-ietf-uri-relative-url-02.txt>, November 1994.
[10] M. Horton and R. Adams. "Standard for interchange of USENET
messages." RFC 1036 (Obsoletes RFC 850), AT&T Bell
Laboratories, Center for Seismic Studies,
<URL:http://ds.internic.net/rfc/rfc1036.txt>, December 1987.
[11] B. Kantor and P. Lapsley. "Network News Transfer Protocol: A
Proposed Standard for the Stream-Based Transmission of News."
RFC 977, UC San Diego, UC Berkeley,
<URL:http://ds.internic.net/rfc/rfc977.txt>, February 1986.
[12] J. Postel. "Simple Mail Transfer Protocol." STD 10, RFC 821,
USC/ISI, <URL:http://ds.internic.net/rfc/rfc821.txt>, August
1982.
[13] J. Postel. "Media Type Registration Procedure." RFC 1590,
USC/ISI, <URL:http://ds.internic.net/rfc/rfc1590.txt>, March
1994.
[14] J. Postel and J. K. Reynolds. "File Transfer Protocol (FTP)."
STD 9, RFC 959, USC/ISI,
<URL:http://ds.internic.net/rfc/rfc959.txt>, October 1985.
[15] J. Reynolds and J. Postel. "Assigned Numbers." STD 2, RFC 1700,
USC/ISI, <URL:http://ds.internic.net/rfc/rfc1700.txt>, October
1994.
[16] T. Berners-Lee, D. Connolly, et al. "HyperText Markup Language
Specification - 2.0." Internet-Draft (work in progress), CERN,
HaL Computer Systems,
<URL:http://www.ics.uci.edu/pub/ietf/html/>, November 1994.
[17] US-ASCII. "Coded Character Set - 7-Bit American Standard Code
for Information Interchange." Standard ANSI X3.4-1986, ANSI,
1986.
14. Authors Addresses
Tim Berners-Lee
Director, W3 Consortium
MIT Laboratory for Computer Science
545 Technology Square
Cambridge, MA 02139, U.S.A.
Tel: +1 (617) 253 9670
Fax: +1 (617) 258 8682
Email: timbl@w3.org
Roy T. Fielding
Department of Information and Computer Science
University of California
Irvine, CA 92717-3425, U.S.A.
Tel: +1 (714) 824-4049
Fax: +1 (714) 824-4056
Email: fielding@ics.uci.edu
Henrik Frystyk Nielsen
World-Wide Web Project
CERN,
1211 Geneva 23, Switzerland
Tel: +41 (22) 767 8265
Fax: +41 (22) 767 8730
Email: frystyk@w3.org
Appendices
These appendices are provided for informational reasons only -- they
do not form a part of the HTTP/1.0 specification.
A. Tolerant Applications
While it may be appropriate for testing applications to verify full
conformance to this specification, it is recommended that
operational applications be tolerant of deviations. This appendix
mentions the most important topics where tolerance is recommended.
A.1 Request-Line, Status-Line, and Header Fields
Clients should be tolerant in parsing the StatusLine and servers
tolerant when parsing the RequestLine. In particular, they should
accept any amount of SP and HTAB characters between fields, even
though only a single SP is specified.
Line terminators for HTTP-header fields should be the sequence
CRLF. However it is recommended that applications, when parsing
such headers, also recognize a single LF as a line terminator and
ignore any leading CR.
Any HTTP-Header which is not recognized should be ignored by
operational applications except when listed in the Mandatory field,
as described in Section 4.3.4.
It is recommended that servers use URIs free of "variant"
characters (whose representation differs in some of the national
variant character sets), punctuation characters, and spaces. This
will make URIs easier to handle by humans when the need arises
(such as for debugging or transmission through non hypertext
systems).
If a Content-Type header is not present in a Object-Header, the
preferred action is to try and guess the media-type by looking at
the first part of the data in the Object-Body. This document does
not provide any algorithm for divining the media-type. If the media-
type cannot be found by guessing, the application can either look
at the file suffix (if a URL is available) or can default to
"application/octet-stream".
A.2 Object Body
As it is not required to convert any Object-Body to a canonical
form regardless of the media-type when transmitted using HTTP, the
client must be very tolerant when parsing Object-Body's of type
"text/*". It is recommended that the following terminators be
considered as line separators:
CR, LF, CRLF
If the line terminator is CRLF, the CR should be ignored.
A.3 Backward Compatibility
Servers should be capable of both accepting Simple-Request's and
generating Simple-Response's. Many dedicated clients will find the
Simple-Request sufficient for their purposes, even though it is
generally recommended to use a Full-Request instead. For more
general purpose client applications, it is recommend the client be
able to generate a Simple-Request, and understand a Simple-Response,
in order to communicate with native HTTP/0.9 servers.
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